Since the 1970s, clean-energy advocates have dreamed of using the sun to split water into oxygen and hydrogen. Such a technique could allow solar energy to be stored as hydrogen fuel for use at nighttime or on cloudy days. But one major obstacle kept this from becoming possible -- until now.

Researchers at Stanford University have had positive results in overcoming this challenge with one solution, and they published their study in Nature Materials this week.

A vision -- and a challenge

The vision has always been to apply a voltage across two electrodes submerged in water, a process which would split water molecules into oxygen and hydrogen.

The technique is a clean-energy dream: it requires only water and electricity and produces pure oxygen and hydrogen.

Hydrogen is the cleanest-burning fuel and has shown promise in a number of renewable energy applications. However, researchers have not been able to overcome a main problem.

"In theory, water splitting is a clean and efficient energy storage mechanism. Unfortunately, solving one problem creates another. The most abundant solar electrodes we have today are made of silicon, a material that corrodes and fails almost immediately when exposed to oxygen, one of the byproducts of the reaction."

The solution

McIntyre and chemist Christopher Chidsey came up with a new approach. They coated their silicon electrodes with a protective, ultra-thin layer of titanium dioxide, which lets in sunlight and can efficiently transfer electricity, while simultaneously protecting the silicon.

In their experiment, the titanium dioxide allowed sunlight to stimulate the photosensitive silicon, which sent electrons flowing into the water, splitting hydrogen from oxygen. The hydrogen gas could then be stored until the sun is not shining. At that point, it could be released to reverse the process and recombined with water to produce electricity.

In their experiments, the researchers found that electrodes without titanium dioxide corroded and failed within a half hour, while the titanium dioxide-coated ones lasted eight hours without corroding or losing efficiency.